I. Field of the Invention
The invention relates to amorphous metal alloys, and more particularly, to amorphous uranium-base alloys in the U-Cr-V system.
II. Description of the Prior Art
Investigations have demonstrated that it is possible to obtain solid amorphous metal alloys from certain compositions. An amorphous substance generally characterizes a non-crystalline or glassy substance, that is, a substance substantially lacking any long range order. In distinguishing an amorphous substance from a crystalline substance, X-ray diffraction measurements are generally suitably employed. Additionally, transmission electron micrography and electron diffraction can be used to distinguish between the amorphous and the crystalline state.
An amorphous metal produces an X-ray diffraction profile in which intensity varies slowly with diffraction angle. Such a profile is qualitatively similar to the diffraction profile of a liquid or ordinary window glass. On the other hand, a crystalline metal produces a diffraction profile in which intensity varies rapidly with diffraction angle.
These amorphous metals exist in a metastable state. Upon heating to a sufficiently high temperature, they crystallize with evolution of a heat of crystallization, and the X-ray diffraction profile changes from one having glassy or amorphous characteristics to one having crystalline characteristics.
It is possible to produce a metal which is totally amorphous or comrpises a two-phase mixture of the amorphous and crystalline state. The term "amorphous metal", as employed herein, refers to a metal which is at least 50 percent amorphous, and preferably 80 percent amorphous, but which may have some fraction of the material present as included crystallites.
Proper processing of certain alloys will produce a metal alloy in the amorphous state. One typical procedure is to cause the molten alloy to be spread thinly in contact with a solid metal substrate such as copper or aluminum so that the molten alloy loses its heat to the substrate. When the molten alloy is spread to a thickness of about 0.002 inch, cooling rates of the order of 10.sup.6 .degree.C/sec are achieved. See, for example, R. C. Ruhl, Vol. 1, Materials Science and Engineering, pp. 313-319 (1967), which discusses the dependence of cooling rates upon the conditions of processing molten alloys. Any process which provides a sufficiently high cooling rate, as on the order of 10.sup.5 to 10.sup.6 .degree.C/sec, can be used. Illustrative examples of procedures which can be used to make the amorphous metal alloys are the rotating double roll procedure described by H. S. Chen and C. E. Miller in Vol. 41, Review of Scientific Instuments, pp. 1237-1238 (1970) and the rotating cylinder technique described by R. Pond, Jr. and R. Maddin in Vol. 245, Transactions of the Metallurgical Society, AIME, pp. 2475-2476 (1969).
In the field of uranium technology, especially involving radiation applications such as reactor fuels, a variety of uranium-base alloys having crystalline or polycrystalline phases have been investigated. Most uranium-base single phase crystalline alloys are generally limited to a total alloying addition of about 5 weight percent. Single phase alloys are preferred for a variety of reason. For example, corrosion of uranium-base fuel is a well-known problem in water-cooled reactors. However, alloys that include elements that are insoluble in uranium (that is, form at least two phases) are less corrosion resistant than alloys that include elements that are soluble in uranium (that is, form a single phase alloy). Thus, in the binary U-Cr system, chromium, which is known to be an excellent corrosion inhibitor, is soluble only up to about 4 atom percent in the high temperature gamma phase at the eutectic temperature of about 859.degree.C. The solubilities of the intermediate temperature beta phase and of the low (room) temperature alpha phase are even lower. This means that the corrosion resistant properties of chromium cannot be sufficiently exploited.
Single phase alloys are also required for optimum resistance to plastic deformation, which in turn depends upon, among other things, high creep resistance and high yield strength. The limited solubility of alloying elements in uranium precludes compositional optimization of these properties. Thermal and radiation stability are also important, and dimensional stability upon exposure to radiation is maximized by an isotropic structure, such as a cubic or pseudocubic (gamma or delta) structure. Cubic structures, however, are not always ideal for resistance to corrosion.
Amorphous metal alloys containing substantial amounts of iron, nickel, cobalt, vanadium and chromium have been described by H. S. Chen and D. E. Polk in a patent application, Ser. No. 318,146, filed Dec. 26, 1972, now U.S. Pat. No. 3,856,513, issued Dec. 24, 1974. While alloys are quite useful for a variety of applications, there is no suggestion that they are useful in nuclear applications. Moreover, recent investigations have shown that many metalloids, such as boron, phosphorus, carbon, silicon and aluminum, and many transition metals, such as iron, nickel, cobalt, titanium and zirconium, do not readily form amorphous alloys with uranium by liquid quenching.
There remains a need to fabricate uranium-base alloys having good mechanical and corrosion resistance properties, consistent with good thermal and dimensional stability.